Interventional techniques are widely used for managing a plurality of potentially life-threatening medical conditions. Generally, interventional techniques may be employed in various fields of medicine such as neurology, general radiology, cardiology and electrophysiology. Specifically, interventional imaging systems may be used to visualize structural information, for example, anatomical details as well as injected contrast, catheters and other devices during an intervention that may be difficult to visualize using other imaging techniques.
Certain medical procedures, however, may also benefit from functional information in addition to structural information for facilitating the interventional procedure. Knowledge of functional information such as tissue perfusion parameters including regional blood volume, regional mean transit time, regional blood flow etc. are very useful in various medical scenarios. A surgeon may rely on these functional parameters for pre-procedure planning of endovascular treatments, for example, concerning cerebral vascular accidents such as a stroke, angioplasties of the carotid and placement of carotidian and intracranial stents. The surgeon may also use the functional parameters during the interventional procedure for evaluating the efficacy of the therapeutic procedure in real-time, and further for determining whether to stop or continue the procedure based on the evaluated effect.
Generally, an interventional procedure may be preceded by an initial patient exam using a magnetic resonance (MR) system or a computed tomography (CT) system for obtaining both structural and functional information for diagnosis and/or treatment. Subsequently, the patient may undergo therapy via an interventional procedure in a vascular operating theater. During the operation, an interventional device such as a catheter may be inserted into a vascular structure, allowing access to a region of interest (ROI), such as vessels of the brain for performing the interventional procedure. The insertion as well as the navigation of the catheter within the different branches of the vascular system, however, is a challenging procedure. Furthermore, use of separate or combined CT/MR systems for structural and functional imaging may involve frequent switching between the different imaging modalities, corresponding movement of patient and change in patient positions, catheter guidance, and/or therapeutic modes. Use of such systems, thus, may lead to complicated workflows and may not be suitable in all imaging scenarios due to size, cost and imaging time constraints.
These limitations are addressed in certain conventional interventional imaging approaches that employ C-arm systems for providing structural and functional information. These C-arm systems may include a source and a detector mounted on a movable arm configured to rotate relative to the center of an imaged volume. Particularly, the C-arm may be configured to move in a desired path so as to orient the source and detector at different positions and angles around a patient disposed on a table for acquiring corresponding projection data, while also allowing a physician to access the patient. In one conventional implementation, for example, the C-arm may be configured to acquire a spin dataset, that is, to rotate axially by about 180 degrees plus the fan angle around the long axis of the patient.
Further, the C-arm system may reconstruct the acquired projection data into two-dimensional (2D) and/or three-dimensional (3D) images using, for example, a filtered back-projection (FBP) or an algebraic reconstruction (ART) technique. The FBP approach, although fast, may introduce streaking artifacts that negatively impact image quality, and in turn, affect medical diagnosis and decision-making. In contrast, iterative methods based on ART may reduce image artifacts by using image priors but may suffer from longer computation times.
The scanning time for a conventional “spin” acquisition that rotates the C-arm around the patient is typically five or more seconds for acquiring sufficient projection data for reconstructing 2D and/or 3D images of desired image quality. Such a slow rotation rate, however, may result in image artifacts due to voluntary motion, such as due to patient repositioning, and involuntary motion such as peristalsis or heart motion within the patient. Additionally, the slow rotation rate may restrict usefulness of a C-arm system for imaging transient phenomena such as perfusion events and/or device motion and guidance. For example, the slow rotation rate of the C-arm system may prove insufficient for imaging dynamic processes that require a faster temporal sampling than, for example, the 5 seconds afforded by a sequence of repeated spin acquisitions.
Moreover, a conventional spin geometry of the C-arm system may further complicate the scanning process as the conventional geometrical configuration entails scanning more than half way around the patient in one or more axial scans. Particularly, in the conventional spin configuration, a radiation source may rotate to positions above the patient table, which may significantly increase a chance of a collision of the C-arm with the table, the patient, other equipment and/or medical devices in the vicinity. Additionally, when positioned above the patient table, the radiation source may cause greater scatter, which in turn, may significantly increase the radiation exposure to the patient and/or a physician. The long scanning time, significant radiation exposure and the complicated workflow, thus, may render use of the conventional C-arm geometry unfeasible for real-time (or near real-time) interventional 3D imaging of dynamic processes.